BACTERIA ASSOCIATED WITH THE TOXIC CYANOBACTERIA NODULARIA SPUMIGENA IN THE BALTIC SEA: LOOKING FOR A POSSIBLE BIOLOGICAL CONTROL ORGANISM

The control of harmful phytoplankton blooms using pathogens has been suggested as a possibility by several authors. In this work, bacteria associated to N. spumigena from the Baltic Sea were characterized by their 16SrDNA gene sequences. Individual cyanobacterial filaments were extensively washed with sterile medium and spread onto nutrient rich agar plates (for isolation and further cultivation) or submitted to direct PCR amplification. The cultivated bacteria were added to exponentially growing N. spumigena cultures and the growth was monitored by in vivo fluorescence. Most of the 16SrDNA sequences obtained from cultured bacteria strains were related to the gamma proteobacteria. Sequences originated from direct PCR amplification on single N. spumigena filaments were related to the gamma proteobacteria and the Cytophaga-Flexibacter group. In laboratory experiments, some bacterial isolates decreased N. spumigena cultures fluorescence up to 40% when compared to cultures with no bacteria addition. However, no acute killing effects were observed on N. spumigena cultures when bacteria were added. The possibility to use these bacteria as biological control for cyanobacterial blooms requires more information about the taxon-specificity of the interactions.